1. Field of the Invention
This invention relates generally to magnetic transducers for reading information signals from a magnetic medium and to methods of making the same.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read (MR) sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an xe2x80x9cMR elementxe2x80x9d) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which the MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., nickel-iron, cobalt, or nickel-iron-cobalt) separated by a layer of nonmagnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., nickel-oxide or iron-manganese) layer.
The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (the signal field). In the SV sensors, SV resistance varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. In addition to the magnetoresistive material, the MR sensor has conductive lead structures for connecting the MR sensor to a sensing means and a sense current source. Typically, a constant current is sent through the MR sensor through these leads and the voltage variations caused by the changing resistance are measured via these leads.
To illustrate, FIG. 1 shows a prior art SV sensor 100 comprising end regions 104 and 106 separated by a central region 102. A free layer (free ferromagnetic layer) 110 is separated from a pinned layer (pinned ferromagnetic layer) 120 by a non-magnetic, electrically-conducting spacer 115. The magnetization of pinned layer 120 is fixed by an antiferromagnetic (AFM) layer 121, which is formed on a gap layer 123 residing on a substrate 180. Cap layer 108, free layer 110, spacer layer 115, pinned layer 120, and AFM layer 121 are all formed in central region 102.
Conventionally, hard magnets are formed in end regions 104 and 106 in order to stabilize free layer 110. These hard magnets are typically formed of a cobalt-based alloy which is sufficiently magnetized and perhaps shielded so that the magnetic fields of the media and/or the write head do not effect the magnetism of the hard magnets. To perform effectively, the hard magnets should have a high coercivity, a high MrT (magnetic remanencexc3x97thickness), and a high in-plane squareness on the magnetization curve. A preferred cobalt-based alloy for the hard magnet is cobalt-platinum-chromium.
Thus, as illustrated in FIG. 1, hard bias layers 130 and 135 are formed in end regions 104 and 106, respectively, and provide longitudinal bias for free layer 110. Leads 140 and 145 are formed over hard bias layers 130 and 135, respectively. Hard bias layers 130 and 135 and lead layers 140 and 145 abut first and second side edges of the read sensor in a connection which is referred to in the art as a xe2x80x9ccontiguous junctionxe2x80x9d. A sensor tail at the contiguous junction is formed from materials such as tantalum, nickel-iron, cobalt-iron, copper, platinum-manganese and ruthenium.
Leads 140 and 145 provide electrical connections for the flow of the sensing current I@s from a current source 160 to the MR sensor 100. Sensing means 170 connected to leads 140 and 145 sense the change in the resistance due to changes induced in the free layer 110 by the external magnetic field (e.g., field generated by a data bit stored on a disk). One material for constructing the leads in both the AMR sensors and the SV sensors is a highly conductive material, such as a metal.
As illustrated in the graph of FIG. 2, the preferred hard magnet material (i.e., cobalt-platinum-chromium) on gap alumina or glass exhibits favorable properties for sensor biasing purposes. As shown, however, these properties degrade when deposited on materials forming the sensor tail in the contiguous junction region (e.g., tantalum, nickel-iron, cobalt-iron, copper, ruthenium, etc.). Unfortunately, if the sensor tail is too long, magnetic instability will result.
Referring ahead to FIG. 9, a close-up view is shown of SV sensor 100 with a contiguous junction 906 and a sensor tail 908. Sensor tail 908 exposes several layers and materials including cobalt-iron 920, ruthenium 922, cobalt-iron 924, copper 926, cobalt-iron 928, nickel-iron 930, tantalum 932, as well as platinum-manganese, iridium-manganese, and nickel-oxide in AFM layer 121 and other materials of a sensor seed layer 918. FIG. 9 illustrates more particularly one approach that was taken to improve the hard magnet properties of hard bias layer 135, which was to include a bi-layer seed layer 910 underneath it. Bi-layer seed layer 910 included a first seed layer 902 consisting of tantalum and a second seed layer 904 consisting of chromium.
Although improved hard magnet properties were exhibited with use of bi-layer seed layer 910 of FIG. 9, relatively thick seed layers (e.g., approximately 30 Angstroms of tantalum and 35 Angstroms of chromium) were required in order to achieve them. Such thick seed layers are undesirable because they increase the spacing between the hard magnet and the free layer, thereby decreasing the effectiveness of the hard magnet.
Accordingly, what are needed are methods and apparatus for improving hard magnet properties in magnetoresistive read heads that do not require the use of thick seed layers.
We have discovered that by utilizing a bi-layered seed layer consisting of oxidized tantalum and chromium over a contiguous junction region of a read sensor, improved hard magnetic properties are exhibited by the hard bias material. In particular, the hard bias material exhibits a high coercivity. Advantageously, the bi-layered seed layer need not be a thick layer but can be relatively thin as the high-level of coercivity achieved is fairly insensitive to the thickness of the tantalum.
More specifically, an inventive magnetic head having improved hard magnet properties includes a read sensor; a multi-layered seed layer formed adjacent the read sensor and over a contiguous junction region of the read sensor; and a hard bias layer formed over the multi-layered seed layer. The multi-layered seed layer includes a first seed layer comprising oxidized tantalum; and a second seed layer comprising chromium. The hard bias layer is made from a cobalt-based alloy, such as cobalt-platinum-chromium. The contiguous junction region exposes one or more sensor materials such as tantalum, nickel-iron, cobalt-iron, copper, platinum-manganese and ruthenium. Preferably, the first seed layer has a thickness of less than 30 Angstroms and the hard bias layer produces a coercivity of about 700 Oersteds or higher. A lead layer may be formed over the hard bias layer.
A magnetic recording device may embody the magnetic head. This magnetic recording device has at least one rotatable magnetic disk; a spindle supporting the at least one rotatable magnetic disk; a disk drive motor for rotating the at least one rotatable magnetic disk; a magnetic head for reading data from the at least one rotatable magnetic disk; and a slider for supporting the magnetic head. The magnetic head has a read sensor; a multi-layered seed layer formed adjacent the read sensor and over a contiguous junction region of the read sensor; and a hard bias layer formed over the multi-layered seed layer. The multi-layered seed layer includes a first seed layer comprising oxidized tantalum; and a second seed layer comprising chromium. The hard bias layer is made from a cobalt-alloy, such as cobalt-platinum-chromium. The contiguous junction region exposes one or more sensor materials such as tantalum, nickel-iron, cobalt-iron, copper, platinum-manganese and ruthenium.
Finally, a method of producing a magnetic head includes the acts of forming an oxidized tantalum seed layer adjacent to a read sensor and over a contiguous junction region of the read sensor by depositing a tantalum layer adjacent to and over the contiguous junction region and then oxidizing the tantalum seed layer to produce the oxidized tantalum seed layer; depositing a chromium seed layer over the oxidized tantalum seed layer; and then depositing a hard bias layer over the chromium seed layer. The contiguous junction region exposes one or more sensor materials such as tantalum, nickel-iron, cobalt-iron, copper, platinum-manganese and ruthenium. The act of depositing the tantalum layer adjacent to and over the contiguous junction region involves depositing a tantalum layer of less than 30 Angstroms. The act of depositing the hard bias layer involves depositing a hard bias layer of cobalt-platinum-chromium. The method may include the further act of depositing a lead layer over the hard bias layer.